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Is it necessary to machine the rotors on the first brake pad change? A mechanic told me it should be done but in the DIY articles and service manuals it does not mention the need to do this (or is it implied?). any information appreciated.

I think your mechanic is concerned about the possibility that your rotors may have some uneven wear on them. Machining them helps even out the surface of the rotors thereby giving them a more even wear from the new pads. Uneven rotors can lead to uneven brake pad wear as well. For rotors to become uneven you would need to have somehow warped them by not changing your pads till the very end. Or have never adjusted your brakes while checking the pads and rotors for wear durring inspection intervals. Usually rotors do not need machining in most circumstances.

Originally posted by Bassethound Is it necessary to machine the rotors on the first brake pad change? A mechanic told me it should be done but in the DIY articles and service manuals it does not mention the need to do this (or is it implied?). any information appreciated.

Machining is not necessary if the rotors are in decent shape and you have no problems with them, such as vibration under braking. Most shops that do rotor machining do not set the equipment up properly or use kids (e.g., Pep Boys) to run the equipment and you end up with thinner rotors and probably more runout than you started with.

You only have 1.6mm of allowable wear, so removing material only serves to shorten the life of the rotor, at best, and at worst, can introduce more problems. Since the rotors are so inexpensive for your platform (assuming ATE, Zimmerman, Balo, Brembo aftermarket) it makes more sense to replace them if they are worn or damaged. Those 300mm x 22mm are not very expensive (except at the dealer parts counter).

Before you install the new pads, check the rotor thickness. If the front rotors are approaching 20.4mm (down from 22mm) then you should consider replacing them.